Myosins constitute a superfamily of motor proteins that convert energy from ATP hydrolysis into mechanical movement along the actin filaments. Phylogenetic analysis currently places myosins into 17 classes based on class-specific features of their conserved motor domain. Traditionally, the myosins have been divided into two classes depending on whether they form monomers or dimers. The conventional myosin of muscle and nonmuscle cells forms class II myosins. They are complex molecules of four light chains bound to two heavy chains that form bipolar filaments via interactions between their coiled-coil tails (type II). Class I myosins are smaller monomeric myosins referred to as unconventional myosins. Now, at least 15 other classes of unconventional myosins are known. How many myosins are needed to ensure the proper development and function of eukaryotic organisms? Thus far, three types of myosins were found in budding yeast, six in the nematode Caenorhabditis elegans, and at least 12 in human. Here, we report on the identification and classification of Drosophila melanogaster myosins. Analysis of the Drosophila genome sequence identified 13 myosin genes. Phylogenetic analysis based on the sequence comparison of the myosin motor domains, as well as the presence of the class-specific domains, suggests that Drosophila myosins can be divided into nine major classes. Myosins belonging to previously described classes I, II, III, V, VI, and VII are present. Molecular and phylogenetic analysis indicates that the fruitfly genome contains at least five new myosins. Three of them fall into previously described myosin classes I, VII, and XV. Another myosin is a homolog of the mouse and human PDZ-containing myosins, forming the recently defined class XVIII myosins. PDZ domains are named after the postsynaptic density, disc-large, ZO-1 proteins in which they were first described. The fifth myosin shows a unique domain composition and a low homology to any of the existing classes. We propose that this is classified when similar myosins are identified in other species.

The loco gene encodes members of a family of RGS proteins responsible for the negative regulation of G-protein signalling. At least two transcripts of loco are expressed in oogenesis, loco-c2 is observed in the anterior-dorsal follicle cells and is downstream of the epidermal growth factor receptor signalling pathway, initiated in the oocyte. loco-c3 is a new transcript of loco, which is expressed in the nurse cells from stage 6 onwards. Analysis of newly generated mutants and antisense technology enabled us to establish that disrupting loco in follicle cells results in ventralized eggs, while disrupting loco in nurse cells results in short eggs, due to defective dumping of the nurse cell cytoplasm into the oocyte.

BackgroundThe loco gene encodes several different isoforms of a regulator of G-protein signalling. These different isoforms of LOCO are part of a pathway enabling cells to respond to external signals. LOCO is known to be required at various developmental stages including neuroblast division, glial cell formation and oogenesis. Less is known about LOCO and its involvement in male development therefore to gain further insight into the role of LOCO in development we carried out a genetic screen and analysed males with reduced fertility.ResultsWe identified a number of lethal loco mutants and four semi-lethal lines, which generate males with reduced fertility. We have identified a fifth loco transcript and show that it is differentially expressed in developing pupae. We have characterised the expression pattern of all loco transcripts during pupal development in the adult testes, both in wild type and loco mutant strains. In addition we also show that there are various G-protein α subunits expressed in the testis all of which may be potential binding partners of LOCO.ConclusionWe propose that the male sterility in the new loco mutants result from a failure of accurate morphogenesis of the adult reproductive system during metamorphosis, we propose that this is due to a loss of expression of loco c3. Thus, we conclude that specific isoforms of loco are required for the differentiation of the male gonad and genital disc.

We have isolated and sequenced a cDNA encoding a predicted 524 amino acid protein from a Drosophila melanogaster ovarian library. Sequence comparisons suggest that this protein encodes a sodium-dependent inorganic phosphate co-transporter similar to a sequence isolated from a rat brain library. In situ hybridisation to messenger RNA in ovaries shows strong expression in germarium at stage 2 of oogenesis. Expression is then weak in follicle cells until stage 10, when high transcript levels are seen in the nurse cells and transferred to the oocyte. This presumably reflects functions in oogenesis and the production of stored mRNAs for use in embryogenesis.

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